Single pole electrical connectors are used in a variety of settings. High power, single pole connectors are used in many industrial settings, and are particularly suitable to situations requiring some degree of portability. In other words, when the electrical system must be transported using a standardized delivery platform (e.g., a standard 18-wheel truck) and then made up on site, single pole connectors are often used. These connectors typically allow for relatively simple installation and break down when a job is completed.
A common type of single pole connector uses mated male and female individual connectors. For example, an electrical supply panel may be used to install a number of panel-mounted connectors. This might be male or female, but in this example, we will assume the panel-mounted connectors are female. Electrical cables extend from the panel to various electrical loads (e.g., large motors, pumps, or other electrical machinery). To connect the cable to the panel, a male cable-end connector is used. This male is inserted into the panel-mounted female connector, thus completing the circuit. When the installation must be broken down, the male cable-end connectors are removed from the female panel-mounted connectors.
Outdoor carnivals and concerts may use these types of connectors to supply electrical power to their various loads. The oil and gas industry, especially land-based operations, often use high power, single pole electrical connectors. In the oil and gas industry, land-based operations often require that all materials be transported via standard 18-wheel trucks. In part for that reason, single pole connectors of the type disclosed herein have become widely used. And because the electrical loads used on land-based oil or gas drilling rigs can be very large, the electrical connectors used are also typically very large. Connectors rated for 1,000 amps or more are common in this industrial setting. Such connectors are physically large, too, sometimes weighing several pounds.
These large single pole electrical connectors have large contacts. For example, a male, single pole electrical connector rated for 1,000 amps or more might have a cylindrical contact surface nearly one inch in diameter and three inches in length. The mated female connector would have an inside diameter matched to that of the outside diameter of the male. These two parts are designed for a very tight fit, to ensure the best possible electrical connection between the male and female contacts. Manufacturing tolerances for these components are typically in the thousandths of an inch.
The prior art design, which was very briefly described above, provides an adequate electrical connection in most situations. But to obtain that electrical connection, the prior art design sometimes requires substantial force to make up the connection. The fit between the male and female connectors is very tight. And with as much a three inches of linear contact surface, the surface friction between the male and female can be quite substantial. Moreover, the surface friction only increases as the connector is made up, because the surface contact between the male and female increases. That fact can make it difficult to fully insert a male connector into a female. When that happens, it can be difficult, if not impossible, to complete the connection.
These types of connectors have various types of locking mechanisms to ensure the male and female connectors remain engaged during use. The locking mechanisms may only be engaged when the male and female connectors are fully engaged, that is, only when the male has been fully inserted into the female. The increasing surface friction described above can make this difficult. And if the male and female components cannot be fully made up, the locking mechanisms may not be usable. When this happens, the connection must be unmade and replaced. Failure to do so (a failure that can and does occur in the field), will result in a live, high power connection that is not locked together. This result can be extremely dangerous, because if a high power single pole connection of the type described herein is pulled apart under power, an enormous spark or arc will be produced. Explosion or fire is possible under such circumstances. The severity of the risk created by this situation cannot be overstated.
On the other hand, it is critical that these types of electrical connectors provide adequate electrical conductivity between the male and female components. If the electrical connection is poor—that is, if there is too much electrical resistance at the contacts—the connection will generate heat (i.e., electrical resistive heating). Given the high current passing through some of these connectors, such heating can be rapid and extreme. It can easily be severe enough to damage, perhaps even break down, the insulation in the connector or on the cable. If the insulation is lost, sparking or arcing can occur, and the same catastrophic results mentioned above may follow.
There are, therefore, two serious risks posed by use of these types of electrical connectors. First, if the extreme surface friction between the male and female components prevents full engagement, an unlocked connection is possible. This can lead to pull out under power, which is extremely dangerous. Second, if the electrical connection between the male and female components is not adequate, extreme heating can occur. This can lead to insulation damage, which is also extremely dangerous.
Reducing one of these risks may increase the other. That is, the surface friction between the male and female contacts may be reduced by increasing the gap between these two components. That is, by relaxing the fit between the male and female, by making it less tight, the surface friction will be reduced, thus making it easier to make up and lock the connections. But relaxing the fit between the male and female may increase the electrical resistance between the contacts, thus leading to excessive resistive heating and the damage that can cause.
On the other hand, resistive heating may be reduced by ensuring the best possible physical engagement between the male and female contacts. To date, this solution has prevailed. High power, single pole electrical connectors tend to maximize the surface contact between the male and female contacts to ensure there is a good electrical connection. This approach, however, results in connectors that are often very difficult to make up in the field. Given that these operations sometimes occur in challenging weather conditions, with workers under pressure to complete the electrical system, it is not surprising to find that some high power, single pole connections are not fully locked prior to use, despite the hazards associated with this situation. Or alternatively, if the electricians are conscientious and make certain that every connection is properly installed and locked, the prior art designs can cause time delays that are very costly to operations.
One alternative to the traditional prior art design discussed above is to use an inserted, multi-piece contact. Such an approach typically involves installation of the multi-piece contact inside the female connector. A recess is machined into the contact surface region of the female connector, and a separate, multi-piece contact is inserted into the recess. The male connector makes primary contact with the multi-piece contact, rather than with the entire length of the female connector's contact region. This approach can greatly reduce the surface friction described above, and can facilitate better connections in field use.
There are, however, some drawbacks to the multi-piece contact design. First, it involves use of a precision, multi-piece contact, in which each individual contact is able to move somewhat independently of the other contacts. This effectively means the contact has many parts that are all able to move. This also means the contact has many, small parts that can break or jam in use. When there are more pieces or parts, there are more chances for failure or breakdown, and the multi-piece contact design is subject to that concern.
The many contacts are typically made of special materials and are subject to very demanding manufacturing specifications. These requirements result in an expensive component, and for this reason, the multi-piece contact approach will increase the cost of the connector. This cost increase can be quite substantial. In some situations, the benefits may justify the higher cost of this design. Nevertheless, a lower-cost design that provides the same or similar benefits would have value in the market.
The multi-piece contact design also creates a compatibility issue. When a multi-piece contact of the type very briefly described above is installed in a female connector, one of two other changes is necessary. The goal of this design is for the multi-piece contact to constitute the sole, or at least primary, contact section. That is, the only area where the female and male connectors will make electrical contact is at the multi-piece contact, which will make contact with an inserted male connector.
To make this work, the fit between the male and female contact regions must be substantially relaxed. Either the inside diameter of the female contact region must be larger or the outside diameter of the male contact must be smaller. Either solution will work, because both will result in much less contact between the general contact surfaces of the male and female connectors. The multi-piece contact installed in the female will extend outward from the rest of the female contact surface area, thus pressing the many individual contacts of the multi-piece contact against part of the male connector. The rest of the male connector's contact surface will make only minimal or intermittent physical contact with the rest of the female connector's contact surface. The primary, perhaps exclusive, area of physical connection within the contact regions will be the multi-piece contact pressing against a relatively small part of the male contact.
Because the fit is greatly relaxed between the male and female connector in this approach, connectors using the multi-piece contact may not be compatible with other designs.
Assume, for example, the male contact diameter is reduced to make the multi-piece contact design work. Such a male connector could not be used with a prior art female connector, because doing so would result in too loose a fit between the male and female. Such a loose fit could result in poor electrical conductivity and the dire results described above. Similarly, if a female connector has an increased inside diameter, it would not work well with prior art male connectors.
This is largely a backward compatibility issue, and it can be quite important. There are thousands of connectors of the general type discussed here in use in the field. If some of those are replaced with a multi-piece contact design of the type described above, there would be incompatible components in use on a single job site. That can be a dangerous situation. There are significant advantages to designs with full backward compatibility. The multi-piece contact solution typically lacks backward compatibility.
For these reasons, there is a need for a simpler, lower-cost solution that provides full backward compatibility. The present invention provides such a solution. To understand the present invention, it is helpful to begin by recognizing the types of electrical resistance present in single pole connectors of the general type discussed here.
Two types of resistance are present: bulk resistance and contact resistance. The bulk resistance is fixed and results from the type of conductor used, the length of the electrical flow path through the conductor, and the size of the conductor. The single pole connectors discussed here use cylindrical core conductors, typically of very low resistance copper. The bulk resistance of such connectors is low, and is proportional to the cross-sectional area of the smallest diameter section of the core conductor.RBαa1 
Where RB represents the bulk resistance and a1 represents the cross-sectional area of the smallest diameter point of the core conductor. The cross-sectional area is proportional to the diameter:a1=πr12 
Where r1 represents the radius of the core conductor at its smallest point. This value will be determined by the size of the connector, with higher current rated connectors having larger core conductors, and thus lower bulk resistance. But for any given connector, the bulk resistance is relatively constant.
The contact resistance is the electrical resistance at the point of physical contact between two connectors. In the single-pole connectors discussed here, the contact resistance is the key concern. This resistance is highly variable, as it depends upon the fit between the male and female contacts, the extent to which oxide layers have formed on the contact surfaces, and so on.
It has been found, however, that contact conductivity (i.e., the inverse of resistance) is generally proportional to the pressure at the point of contact between the male and female contact surfaces.CCαPC 
Where CC represents the contact conductivity (i.e., the inverse of resistance) and PC represents the pressure at the point of contact. The pressure depends upon the force and the contact area, as follows:PC=FC/AC 
Where FC represents the normal force at the point of contact and AC represents the contact surface area. The area in this equation is a surface area, not a cross-sectional area. The capital “A” is used in this equation to emphasize this point.
Given these principles, it can be seen that the contact conductivity is proportional to the normal force and is inversely proportional to the contact surface area. The first point is intuitive. The more force pressing the contact surfaces together, the greater the electrical conductivity (i.e., less electrical resistance) between the contacts. This intuitive result is driven by at least two important physical results of the increased force. First, when more force is exerted, the many, tiny peaks and valleys on the actual contact surfaces are pressed against each other, thus resulting in more actual physical contact between the two surfaces. Second, when more force is exerted, any film layers (e.g., dirt, grease, or oxides) are reduced or eliminated at the points of contact.
The second point that follows from this equation, however, is counter intuitive, at least when working in the area of high-power, single-pole electrical connectors. The contact conductivity is inversely proportional to the contact surface area. This means that as the contact surface area decreases, the conductivity increases. In theory, this would mean a very small contact point between the male and female connectors would result in the maximum contact conductivity. And for small current signals, this result generally holds. But for large currents, there are limits to the application of this principle.
A large part of the contact resistance in high-power connectors is constriction resistance, which depends upon the actual physical contact area. If the points of physical contact are reduced too much, the current flow becomes constricted at the point of contact, and contact resistance increases. How much contact area is needed depends on how large the currents are within the connectors. For high-power, single-pole connectors of the type discussed here, constriction resistance limits how small the contact area may be.
A practical, working set of limits for these variables has been determined. These connectors are typically rated based on the sizing of the core conductors. Thus, the ratings of these connectors depend primarily on the bulk resistance, which varies with the cross-section area of the smallest diameter point of the core conductor. It follows, therefore, that the contact resistance should remain equal to or less than the bulk resistance. Otherwise, the contact resistance could become limiting, and in use, could result in overall resistance values that are too high, values that could result in excessive resistive heating of the connection.
It has been determined that by maintaining the total contact surface area within about 25% of the cross-sectional area of the smallest point of the core conductor, the contact resistance will remain approximately equal to or less than the bulk resistance of the connector. In other words, by ensuring that the total contact surface area is at least 75% of the cross-sectional area of the smallest point of the core conductor, satisfactory performance is ensured. To be fully clear, satisfactory performance is defined here as maintaining the contact resistance at or below the bulk resistance of the connector's core conductor. As long as this relationship exists, the contact resistance is not limiting.
These findings are highly significant, because they allow for a much smaller contact region than has been used in prior art connectors. Where a typical prior art connector may have male and female contact regions that are between two and three inches in length, the current invention is able to use a male contact surface that is substantially less than one inch in length, while maintaining the contact resistance within reasonable limits. This result is highly advantageous because it greatly reduces the sliding surface friction between the male and female contacts. With less friction, less force is needed to make up the connections. These beneficial results are obtained through use of a simple, single-piece contact that is fully backward compatible.
The sliding friction concern discussed above (i.e., the difficulty in making up or breaking down these connectors due to the tight fit between male and female connectors) can be reduced in two ways. First, the force between the contacts may be reduced. This can be done by relaxing the tight fit between the male and female, either by changing manufacturing specifications or by reducing the outward spring tension on the internal spring of the male contact (more fully discussed in connection with FIGS. 7-8 below). Second, the area of physical contact may be reduced. If there is less contact area between the male and female contacts, there will be less sliding friction between them.
The present invention allows use of both. The goal is to maintain acceptable contact conductivity. If the normal force between the contacts is reduced, the contact conductivity decreases. If the contact surface area decreases, the contact conductivity increases. Thus, it is possible to maintain acceptable contact conductivity by reducing both the normal force and the contact surface area. These two changes have a cumulative effect on the contact sliding friction, but have counter effects on the contact conductivity.
The present invention, in a preferred embodiment, is a single-pole, male electrical connector having a generally cylindrical core conductor with a minimum cross-section area of a1, a contact surface with an effective surface area of ACeff, wherein ACeff≧0.75 a1. In a preferred embodiment, the contact surface is generally cylindrical and smooth, such that AC=πdClC, where dC represents the diameter of the contact region and lC represents the axial length of the contact surface. In this embodiment, ACeff=AC. When these equations are combined for this embodiment, we see that:πdClC≧0.75πr12 
It follows, therefore, that,lC≧0.75r12/dC 
To use sample figures, assume the minimum core conductor diameter is 1 inch, and the contact diameter is 1.05. For a male contact with these dimensions, the contact surface length should be at least approximately 0.18 inch. Compare that to a prior art male contact surface of two to three inches in length. The male contact may be of any size beyond this minimum, so long as the contact is short enough to substantially reduce the sliding friction between the male and female contacts.
In another embodiment, the contact surface is irregular, with grooves or other cuttings made into its surface. In such an embodiment, the effective surface area is ACeff=AC−AREM, where AREM represents the portion of the contact surface area removed. This embodiment is described in more detail below, and a sample calculation is provided.